[Elecraft] K3 Roofing filters

[Joe Subich, W4TV]

Unlike many other transceivers, ultimate selectivity in the K3 is not
determined by the crystal filter.  Ultimate selectivity is determined
by the DSP whilst the roofing filter only impacts narrow band dynamic
range (the level of "close in" signals applied to the second mixer and
analog to digital converter [ADC]).  In this case, the "roofing" filter
sets the maximum bandwidth of the receive chain.  See discussions by
Elecraft here: http://www.elecraft.com/K3/Roofing_Filters.htm

My experience leads me to recommend the standard 2.7 KHz (5 pole) for
SSB (based on the"exchange" price) with the added $130 spent on a 2.1
or 1.8 KHz filter if necessary.  For CW and digital I would choose 400
Hz as the primary filter (the 500 Hz INRAD if one uses some of the 500
Hz wide MFSK based modes) and the 200 Hz 5 pole for critical CW (or
possibly PSK31 and JT9) in the presence of strong adjacent signals.

I don't see the need for a 1000 or 700 Hz filter as when conditions
allow "wide" scanning, one of the SSB filters is generally sufficient
in combination with DSP set to 1000/800/700 Hz.

73,

    ... Joe, W4TV


On 8/6/2013 5:37 AM, g3izd at sky.com wrote:
> I am about to purchase a K3 (k). My main interest is certainly CW
> with
occasional forays into SSB and even data, and I note the selection of
roofing filters available, no doubt the 8-pole are somewhat better but
what is the general feeling regarding the bandwidth(s) to be included.
> Ivan G3IZD
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